The present invention relates to a method and structure for connecting a terminal with a wire in which a tubular wire connecting portion of a terminal is crimp-connected to a core of a wire in a uniform manner over the whole circumference by using, for example, a rotary swaging machine.
Conventionally, a wire is connected to a terminal by the following connecting method. As shown in FIGS. 21A and 14B, for example, a core 37 of a wire 35 is crimped by a pair of crimp pieces 34 which are erected from both sides of a bottom plate 36 of a terminal 33, and the paired crimp pieces 34 are crimpingly deformed into a substantially eyeglasses-like shape, whereby the core 37 is strongly pressed from both the sides and tip ends 34a of the crimp pieces 34 are caused to bite the middle area of the core 37. As a result, the contact between the core 37 and the crimp pieces 34 is attained. As shown in FIG. 21B, inside the crimp pieces 34, the diameter of the core 37 is reduced, and, in the front and rear end sides of the crimp pieces 34, the diameter of the core 37 is outward increased, so that the core 37 is crimped by the wedge function.
The connecting method using the pair of crimp pieces 34 is effective for the wire 35 of a small diameter. By contrast, for a wire of a large diameter such as a shielded wire through which a large current can be flown, the method has a problem in that the contact area between the crimp pieces 34 and the core is small and the electric resistance is easily increased.
Therefore, a terminal of a type in which a core is crimped equally in the circumferential direction is used for such a wire of a large diameter. As an example of a connecting method using such a terminal, FIG. 22 shows a method of connecting a terminal with a wire which is disclosed in Japanese Utility Model Publication No. 43746/1975.
In the connecting method, under a state where a core of a wire is inserted into a tubular wire connecting portion of a terminal, the tubular wire connecting portion is crimped into a hexagonal shape by a pair of upper and lower dies 21, to cause the core 23 to be closely contacted into the wire connecting portion 22. As shown in FIG. 23, each of the dies 21 has three pressing faces 24, and a center ridge 25 is formed on each of the pressing faces 24. As shown in FIG. 22, the ridges 25 radially press the centers of the outer faces of the hexagonal wire connecting portion 22 to enhance the contact performance between the core 23 of the wire and the wire connecting portion 22 of the terminal.
However, the conventional connecting method and the connecting structure using the method have a problem in that, as shown in FIG. 22, burrs 26 are easily produced between the upper and lower dies 21 and on both sides of the wire connecting portion 22, and a large manpower is required for removing the burrs 26. When the wire connecting portion 22 of the terminal is crimped by using the upper and lower dies 21, as shown in FIG. 24, the vertical crimp forces (internal stress) P1 which are directed to the center of the core 23 largely act, and the crimp forces (internal stress) P2 on the lateral portions tend to be reduced, thereby causing another problem in that a gap is easily formed on both sides of the wire connecting portion 22 and between the element wires of the core 23, or between the core 23 and the wire connecting portion 22. When such a gap is formed, the electric resistance is increased to produce the possibilities that the power transmission efficiency is lowered, and that the connecting portion is overheated.
FIG. 25 shows a mode of crimp-connection of a wire by using a method similar to that of FIG. 22. The ridges 25 of the dies 21 (FIG. 23) radially press a core 23xe2x80x2 of a wire at six places as indicated by the arrows F. Therefore, the core 23xe2x80x2 is deformed so as to have a tortoise-like section shape, and stress concentration (the chain lines 29 show the distribution of internal stress) occurs in regions of a wire connecting portion 22xe2x80x2 of a terminal which are between recesses 27 due to the ridges 25 (FIG. 23), i.e., in the vicinities of convex portions 28, and the crimping on the core 23xe2x80x2 becomes uneven in the circumferential direction. As a result, gaps (gaps between element wires) 30 are easily formed in the core 23xe2x80x2, gaps 31 are easily formed also between: the core 23xe2x80x2 and the wire connecting portion 22xe2x80x2 of the terminal, and the wire connecting portion 22xe2x80x2 tends to crack because of the stress concentration, thereby producing a problem in that the strength is reduced. When the gaps 30 and 31 are formed, the electric resistance is increased in the same manner as described above to produce the possibilities that the power transmission efficiency is lowered, and that the connecting portion is overheated. Moreover, there is a further possibility that the core 23xe2x80x2 easily slips from the wire connecting portion 22xe2x80x2.
In view of the above-discussed problems, it is an object of the invention to provide a method and structure for connecting a terminal with a wire in which a tubular wire connecting portion of a terminal can be beautifully crimped to a wire with producing internal stress uniformly in the circumferential direction, and without producing burrs, gaps between element wires of a core of the wire, and between the core and the wire connecting portion of the terminal can be eliminated to enhance the reliability of the electrical connection between the terminal and the wire, and the mechanical strength of the connecting portion can be improved.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A method of connecting a terminal with a wire comprising the steps of:
inserting a core of the wire into a tubular wire connecting portion of the terminal; and
crimping the wire connecting portion in a radial direction of the wire so that the wire connecting portion is compressed in the radial direction and uniformly over a whole circumference of the wire.
(2) The method according to (1), wherein the wire connecting portion is compressed by dies in the radial direction over the whole circumference while rotating the dies by using a rotary swaging machine.
(3) The method according to (1), wherein
a protrusion is formed on an outer periphery of the wire connecting portion, and
during circumferential crimping of the wire connecting portion, the protrusion is projected from an inner periphery of the wire connecting portion to bite the core.
(4) A structure for connecting a terminal with a wire wherein a core of the wire is inserted into a tubular wire connecting portion of the terminal, and the wire connecting portion is crimped in a radial direction of the wire so that the wire connecting portion is compressed in the radial direction and uniformly over a whole circumference of the wire and an outer periphery of a compressed part of the wire connecting portion has a true circular section shape.
(5) The structure according to (4), wherein
a protrusion is formed on an outer periphery of the wire connecting portion, and
the protrusion is projected from an inner periphery of the wire connecting portion to bite the core after the wire connecting portion is crimped.
(6) The structure according to (5), wherein the protrusion is an annular ridge or at least one projection.
(7) A terminal comprising:
a wire connecting portion including a wire insertion hole, the wire connecting portion being to be subjected to a circumferential crimping process; and
a contact protrusion, for entering a core of a wire, elongating in, a longitudinal direction of a wire and disposed in the wire insertion hole.
(8) The terminal according to (7), wherein the contact protrusion is positioned at a center of the wire insertion hole.
(9) The terminal according to (7), wherein the contact protrusion has a columnar shape.
(10) The terminal according to (7), wherein the contact protrusion has an initial length which is substantially one third of a length of the wire insertion hole.
(11) A method of connecting a core of a wire with a terminal including a wire connecting portion including a wire insertion hole, and a contact protrusion elongating in a longitudinal direction of a wire and disposed in the wire insertion hole, the method comprising the steps of:
inserting the core into the wire insertion hole so that the contact protrusion enters the core; and
crimping the wire connecting portion radially and uniformly over a whole circumference at the end by a circumferential crimping unit.